Add test for unknown Xcode version string (#10979)

Also, correct an existing test description.

packages/flutter_tools/test/ios/mac_test.dart

@@ -100,7 +100,7 @@ void main() {
       ProcessManager: () => mockProcessManager,
     });
 
-    testUsingContext('xcodeVersionText returns null when xcodebuild is not installed', () {
+    testUsingContext('xcodeVersionText returns formatted version text', () {
       when(mockProcessManager.runSync(<String>['/usr/bin/xcodebuild', '-version']))
           .thenReturn(new ProcessResult(1, 0, 'Xcode 8.3.3\nBuild version 8E3004b', ''));
       expect(xcode.xcodeVersionText, 'Xcode 8.3.3, Build version 8E3004b');
@@ -108,6 +108,14 @@ void main() {
       ProcessManager: () => mockProcessManager,
     });
 
+    testUsingContext('xcodeVersionText handles Xcode version string with unexpected format', () {
+      when(mockProcessManager.runSync(<String>['/usr/bin/xcodebuild', '-version']))
+          .thenReturn(new ProcessResult(1, 0, 'Xcode Ultra5000\nBuild version 8E3004b', ''));
+      expect(xcode.xcodeVersionText, 'Xcode Ultra5000, Build version 8E3004b');
+    }, overrides: <Type, Generator>{
+      ProcessManager: () => mockProcessManager,
+    });
+
     testUsingContext('eulaSigned is false when clang is not installed', () {
       when(mockProcessManager.runSync(<String>['/usr/bin/xcrun', 'clang']))
           .thenThrow(const ProcessException('/usr/bin/xcrun', const <String>['clang']));